During the last year over 400 peptides have been produced by a PRI contract facility managed by the Branch and within the Branch itself. These peptides have supported research projects in nearly all Laboratories of the NIAID. Synthetic peptides have been used to define and study cytotoxic T lymphocyte or helper T cell epitopes for HIV, rotavirus, influenza virus, chlamydia, ovalbumin, myelin basic protein and heat shock proteins. Synthetic peptides have been used to prepare antisera against proteins originally described by protein or nucleic acid sequence analysis. Such antisera have been prepared against the proteins from the following sources: vacinnia virus, respiratory syncytial virus, MAIDS virus, cowpox virus, dengue virus, HIV, Plasmodium falciparum, rat cyclophilin/PPIase, T cell activation proteins, MHC class II DR and DP molecules, and FcEpsilon receptors. In addition, peptides have been prepared to study chemotaxis and to mimic the activity of TAT from the HIV virus. Within the Branch, synthetic peptides were used to map the H-2 restricted cytotoxic T-lymphocyte epitopes on Simian Virus 40 (SV40) T antigen. Five distinct CTL recognition sites were identified in the SV40 T antigen, four of these were HD\-2Db restricted and one was H-2Kb restricted. Three of the four H-2Db sites were clustered in the amino terminal half of the large T antigen. Evidence was obtained indicating that the synthetic peptides did not completely mimic the activity of endogenously processed large T antigen.